Composition for producing tagatose and method of producing tagatose using the same

ABSTRACT

Provided are a composition for producing tagatose, comprising fructose-6-phosphate 4-epimerase, and a method of producing tagatose using the same.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of International Application No.PCT/KR2018/003749, filed Mar. 30, 2018, which claims the benefit ofKorean Application No. 10-2017-0042165, filed Mar. 31, 2017, thecontents of which are hereby incorporated by reference in theirentirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to a composition for producingtagatose-6-phosphate, comprising fructose-6-phosphate 4-epimerase, and amethod of producing tagatose using the same.

2. Description of the Related Art

Conventional methods of producing tagatose include a chemical method (acatalytic reaction) and a biological method (an isomerization enzymereaction) of using galactose as a main raw material (see Korean PatentNo. 10-0964091). However, the price of lactose which is a basic rawmaterial of galactose used as a main raw material in the knownproduction methods is unstable, depending on produced amounts, supply,and demand of raw milk and lactose in global markets, etc. Thus, thereis a limitation in the stable supply thereof. To overcome the problem ofthe conventional methods of producing tagatose, methods of producingtagatose from D-fructose having a low price and steady supply usinghexuronate C4-epimerase have been reported (2011. Appl BiochemBiotechnol. 163:444-451; Korean Patent No. 10-1550796). However, thereis a limitation in that the isomerization has a low conversion rate.

Tagatose-bisphosphate aldolase (EC 4.1.2.40) is known to produceglycerone phosphate and D-glyceraldehyde 3-diphosphate from D-tagatose1,6-bisphosphate as a substrate, as in the following [Reaction Scheme1], and to participate in a galactose metabolism. However, there havebeen no studies regarding whether the tagatose-bisphosphate aldolase hasactivity to convert fructose-6-phosphate into tagatose-6-phosphate.D-tagatose 1,6-bisphosphate⇔glycerone phosphate+D-glyceraldehyde3-diphosphate  [Reaction Scheme 1]

Under this background, the present inventors have conducted extensivestudies to develop an enzyme which may be used in the production oftagatose, and as a result, they found that tagatose-bisphosphatealdolase (EC 4.1.2.40) has the ability to convert glucose-6-phosphateinto tagatose-6-phosphate, thereby completing the present disclosure.

Accordingly, glucose or starch may be used as a raw material tosequentially produce glucose-1-phosphate and glucose-6-phosphate, andthen tagatose-bisphosphate aldolase of the present disclosure may beused to convert glucose-6-phosphate into tagatose-6-phosphate, andtagatose-6-phosphate phosphatase which performs an irreversible reactionpathway may be used to produce tagatose while remarkably increasing aconversion rate of glucose or starch into tagatose.

SUMMARY OF THE INVENTION

An object of the present disclosure is to provide a composition usefulfor the production of tagatose-6-phosphate, comprisingtagatose-bisphosphate aldolase, a microorganism expressing thetagatose-bisphosphate aldolase, or a culture of the microorganism.

Another object of the present disclosure is to provide a compositionuseful for the production of tagatose, comprising tagatose-bisphosphatealdolase, a microorganism expressing the tagatose-bisphosphate aldolase,or a culture of the microorganism; and tagatose-6-phosphate phosphatase,the microorganism expressing the tagatose-6-phosphate phosphatase, or aculture of the microorganism.

Another object of the present disclosure is to provide a method ofproducing tagatose, comprising converting fructose-6-phosphate intotagatose-6-phosphate by contacting fructose-6-phosphate withtagatose-bisphosphate aldolase, a microorganism expressing thetagatose-bisphosphate aldolase, or a culture of the microorganism,wherein the method may further comprise converting tagatose-6-phosphateinto tagatose by contacting tagatose-6-phosphate withtagatose-6-phosphate phosphatase, a microorganism expressing thetagatose-6-phosphate phosphatase, or a culture of the microorganism.

Other objects and advantages of the present disclosure will be describedin more detail with reference to the following description along withthe accompanying claims and drawings. Since contents that are notdescribed in the present specification may be sufficiently recognizedand inferred by those skilled in the art or similar art, a descriptionthereof will be omitted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1D are results of HPLC chromatography showing thattagatose-bisphosphate aldolases (CJ_KO_F6P4E, CJ_RM_F6P4E, CJ_RP_F6P4E,and CJ_LP_F6P4E) of one embodiment of the present disclosure havefructose-6-phosphate-4-epimerase activity;

FIGS. 2A and 2B are results of HPLC chromatography showing thattreatment of fructose-6-phosphate with tagatose-bisphosphate aldolase(CJ_KO_F6P4E and CJ_RP_F6P4E) and tagatose-6-phosphate phosphatase(CJ_T4) converts fructose-6-phosphate into tagatose in one embodiment ofthe present disclosure;

FIG. 3 is a result of HPLC chromatography showing that T4 which is anenzyme of one embodiment of the present disclosure hastagatose-6-phosphate phosphatase activity;

FIG. 4 is a result of protein electrophoresis (SDS-PAGE) to analyzemolecular weights of enzymes used in the production pathways of tagatosefrom starch, sucrose, or glucose in one embodiment of the presentdisclosure, wherein M represents a protein size ladder (size marker,Bio-RAD, USA);

FIG. 5 is a result of HPLC chromatography showing that TD1(CJ_TD1_F6P4E)which is an enzyme of one embodiment of the present disclosure hasfructose-6-phosphate-4-epimerase activity; and

FIG. 6 is a result of HPLC chromatography showing that when all of theenzymes involved in the production pathway of tagatose from maltodextrinwere added at the same time, tagatose was produced by complex enzymereactions, wherein CJ_AN1_F6P4E was used as tagatose-6-phosphate kinase;

FIG. 7 is a result of HPLC chromatography showing that T4 which is anenzyme of the present disclosure has tagatose-6-phosphate phosphataseactivity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present disclosure will be described in detail asfollows. Meanwhile, each description and embodiment disclosed in thisdisclosure may be applied to other descriptions and embodiments tocommon things. Further, all combinations of various elements disclosedin this disclosure fall within the scope of the present disclosure.Further, the scope of the present disclosure is not limited by thespecific description described below.

To achieve one object of the present disclosure, an aspect of thepresent disclosure provides a composition for producingtagatose-6-phosphate, comprising tagatose-bisphosphate aldolase, amicroorganism expressing the tagatose-bisphosphate aldolase, or aculture of the microorganism.

The tagatose-bisphosphate aldolase (EC 4.1.2.40) is known to produceglycerone phosphate and D-glyceraldehyde 3-diphosphate from D-tagatose1,6-bisphosphate as a substrate, and to participate in a galactosemetabolism. For example, the tagatose-bisphosphate aldolase may be anyone without limitation as long as it is able to producetagatose-6-phosphate from fructose-6-phosphate as a substrate.

Specifically, the tagatose-bisphosphate aldolase may be a polypeptideconsisting of an amino acid sequence of SEQ ID NO: 1, 3, 5, 7, or 9, orcomprise a polypeptide having at least 80%, 90%, 95%, 97%, or 99%homology with the amino acid sequence of SEQ ID NO: 1, 3, 5, 7, or 9. Itis also apparent that a polypeptide having the homology and an aminoacid sequence exhibiting the efficacy (i.e., fructose-6-phosphateC4-epimerization activity to convert fructose-6-phosphate intotagatose-6-phosphate by epimerizing fructose-6-phosphate at C4 positionof fructose) corresponding to the protein consisting of the amino acidsequence of SEQ ID NO: 1, 3, 5, 7, or 9 is also included in the scope ofthe present disclosure, although it has an amino acid sequence, of whicha partial sequence is deleted, modified, substituted, or added. Further,a probe which may be produced from the known nucleotide sequence, forexample, a polypeptide encoded by a polynucleotide which is hybridizablewith a complementary sequence to all or a part of a nucleotide sequenceencoding the polypeptide under stringent conditions may be also includedwithout limitation, as long as it has the fructose-6-phosphateC4-epimerization activity. Therefore, the composition for producingtagatose-6-phosphate may further comprise fructose-6-phosphate. Further,the composition may comprise one or more of tagatose-bisphosphatealdolase consisting of the amino acid sequence of 1, 3, 5, 7, or 9.

The present disclosure revealed that the ‘tagatose-bisphosphatealdolase’ exhibits the fructose-6-phosphate 4-epimerization activity toconvert fructose-6-phosphate into tagatose-6-phosphate by epimerizingfructose-6-phosphate at C4 position. In the present disclosure,therefore, the ‘tagatose-bisphosphate aldolase’ may be usedinterchangeably with ‘fructose-6-phosphate C4 epimerase’.

As used herein, the term “stringent conditions” means conditions underwhich specific hybridization between polynucleotides is allowed. Theseconditions depend on the length of the polynucleotide and the degree ofcomplementation, and variables are well known in the art, andspecifically described in a literature (e.g., J. Sambrook et al.,infra). The stringent conditions may include, for example, conditionsunder which genes having high homology, 80% or higher homology, 90% orhigher homology, 95% or higher homology, 97% or higher homology, or 99%or higher homology, are hybridized with each other and genes havinghomology lower than the above homology are not hybridized with eachother, or ordinary washing conditions of Southern hybridization, i.e.,washing once, specifically, twice or three times at a salt concentrationand a temperature corresponding to 60° C., 1×SSC, 0.1% SDS,specifically, 60° C., 0.1×SSC, 0.1% SDS, and more specifically 68° C.,0.1×SSC, 0.1% SDS. The probe used in the hybridization may be a part ofa complementary sequence of the nucleotide sequence. Such a probe may beproduced by PCR using oligonucleotides produced based on the knownsequence as primers and a DNA fragment containing these nucleotidesequences as a template. Further, those skilled in the art may adjustthe temperature and the salt concentration of the washing solutionaccording to factors such as the length of the probe, if necessary.

As used herein, the term “homology” refers to a percentage of identitybetween two polypeptide moieties. Sequence correspondence from onemoiety to another may be determined by a known technique in the art. Forexample, the homology may be determined by directly aligning thesequence information of two polypeptide molecules, e.g., parameters suchas score, identity, and similarity, etc., using a computer program thatis readily available and capable of aligning sequence information (e.g.,BLAST 2.0). Additionally, the homology between polynucleotides may bedetermined by hybridizing the polynucleotides under a condition forforming a stable double-strand in the homologous regions followed bydigesting the hybridized strand by a single-strand-specific nuclease todetermine the size of digested fragments.

In a specific embodiment, the fructose-6-phosphate-4-epimerase of thepresent disclosure may be an enzyme derived from a thermophilicmicroorganism or a variant thereof, for example, an enzyme derived fromThermanaerothrix sp. or a variant thereof, an enzyme derived fromKosmotoga sp. or a variant thereof, an enzyme derived from Rhodothermussp. or a variant thereof, an enzyme derived from Limnochorda sp. or avariant thereof, and specifically, an enzyme derived fromThermanaerothrix daxensis, Kosmotoga olearia, Rhodothermus marinus,Rhodothermus profundi, or Limnochorda pilosa, but is not limitedthereto.

The fructose-6-phosphate-4-epimerase of the present disclosure or avariant thereof is characterized by converting D-fructose-6-phosphateinto D-tagatose-6-phosphate by epimerizing D-fructose-6-phosphate at C4position. The fructose-6-phosphate-4-epimerase of the present disclosuremay be an enzyme which is known to have tagatose-bisphosphate aldolaseactivity, and the tagatose-bisphosphate aldolase produces glyceronephosphate and D-glyceraldehyde 3-diphosphate from D-tagatose1,6-bisphosphate as a substrate, and participates in a galactosemetabolism. The present disclosure newly revealed that thetagatose-bisphosphate aldolase has the fructose-6-phosphate-4-epimeraseactivity. Accordingly, one embodiment of the present disclosure relatesto novel use of the tagatose-bisphosphate aldolase including using thetagatose-bisphosphate aldolase as the fructose-6-phosphate-4-epimerasein the production of tagatose-6-phosphate from fructose-6-phosphate.Further, another embodiment of the present disclosure relates to amethod of producing tagatose-6-phosphate from fructose-6-phosphate usingthe tagatose-bisphosphate aldolase as thefructose-6-phosphate-4-epimerase.

In one embodiment, the fructose-6-phosphate-4-epimerase of the presentdisclosure may be an enzyme having high heat resistance. Specifically,the fructose-6-phosphate-4-epimerase of the present disclosure mayexhibit 50% to 100%, 60% to 100%, 70% to 100%, or 75% to 100% of itsmaximum activity at 50° C. to 70° C. More specifically, thefructose-6-phosphate-4-epimerase of the present disclosure may exhibit80% to 100% or 85% to 100% of its maximum activity at 55° C. to 65° C.,60° C. to 70° C., 55° C., 60° C., or 70° C.

Furthermore, the fructose-6-phosphate-4-epimerase consisting of theamino acid sequence of SEQ ID NO: 1, 3, 5, 7, or 9 may be, but is notlimited to, encoded by a nucleotide sequence of SEQ ID NO: 2, 4, 6, 8,or 10, respectively.

The fructose-6-phosphate-4-epimerase of the present disclosure or avariant thereof may be obtained by transforming a microorganism such asEscherichia.coli with DNA expressing the enzyme of the presentdisclosure or the variant thereof, e.g., SEQ ID NO: 2, 4, 6, 8, or 10,culturing the microorganism to obtain a culture, disrupting the culture,and then performing purification using a column, etc. The microorganismfor transformation may include Corynebacterium glutamicum, Aspergillusoryzae, or Bacillus subtilis, in addition to Escherichia.coli. In aspecific embodiment, the transformed microorganism may beEscherichia.coli BL21(DE3)/CJ_KO_F6P4E, Escherichia.coliBL21(DE3)/CJ_RM_F6P4E, Escherichia.coli BL21(DE3)/CJ_RP_F6P4E,Escherichia.coli BL21(DE3)/CJ_LP_F6P4E, or Escherichia.coliBL21(DE3)/pBT7-C-His-CJt_d1. These microorganisms were deposited at theKorean Culture Center of Microorganisms which is an InternationalDepositary Authority under the provisions of the Budapest Treaty withAccession No. KCCM11999P (Escherichia.coli BL21(DE3)/CJ_KO_F6P4E) (dateof deposit: Mar. 24, 2017), KCCM12096P (Escherichia.coliBL21(DE3)/CJ_RM_F6P4E) (date of deposit: Aug. 11, 2017), KCCM12097P(Escherichia.coli BL21(DE3)/CJ_RP_F6P4E) (date of deposit: Aug. 11,2017), KCCM12095P (Escherichia.coli BL21(DE3)/CJ_LP_F6P4E) (date ofdeposit: Aug. 11, 2017), and KCCM11995P (Escherichia.coliBL21(DE3)/pBT7-C-His-CJ_td1) (date of deposit: Mar. 20, 2017),respectively.

The fructose-6-phosphate-4-epimerase used in the present disclosure maybe provided by using a nucleic acid encoding the same.

As used herein, the term “nucleic acid” means that it encompasses DNA orRNA molecules, wherein nucleotides which are basic constituent units inthe nucleic acid may include not only natural nucleotides but alsoanalogues with modification of sugar or base (see: Scheit, NucleotideAnalogs, John Wiley, New York (1980); Uhlman and Peyman, ChemicalReviews, 90:543-584(1990)).

The nucleic acid of the present disclosure may be a nucleic acidencoding the polypeptide consisting of the amino acid sequence of SEQ IDNO: 1, 3, 5, 7, or 9 of the present disclosure or a nucleic acidencoding a polypeptide having at least 80%, 90%, 95%, 97% or 99%homology with the fructose-6-phosphate-4-epimerase of the presentdisclosure and having the fructose-6-phosphate-4-epimerase activity. Forexample, the nucleic acid encoding the fructose-6-phosphate-4-epimeraseconsisting of the amino acid sequence of SEQ ID NO: 1 may be a nucleicacid having at least 80%, 90%, 95%, 97%, 99% or 100% homology with thenucleotide sequence of SEQ ID NO: 2. Further, the nucleic acid encodingthe fructose-6-phosphate-4-epimerase consisting of the amino acidsequence of SEQ ID NO: 3, 5, 7, or 9 may be a nucleic acid having atleast 80%, 90%, 95%, 97%, 99% or 100% homology with the nucleotidesequence of SEQ ID NO: 4, 6, 8, or 10 corresponding thereto,respectively. It is also apparent that the nucleic acid of the presentdisclosure may include a nucleic acid which is translated into thefructose-6-phosphate-4-epimerase of the present disclosure due to codondegeneracy or a nucleic acid which hybridizes with a nucleic acidconsisting of a nucleotide sequence complementary to the nucleotidesequence of SEQ ID NO: 2, 4, 6, 8, or 10 under stringent conditions andencodes the polypeptide having the fructose-6-phosphate-4-epimeraseactivity of the present disclosure.

The microorganism expressing the fructose-6-phosphate-4-epimerase whichmay be used in the present disclosure may be a microorganism comprisinga recombinant vector comprising the nucleic acid.

The vector may be operably linked to the nucleic acid of the presentdisclosure. As used herein, the term “operably linked” means that anucleotide expression regulatory sequence and a nucleotide sequenceencoding a targeted protein are operably linked to each other to performthe general functions, thereby affecting expression of the encodingnucleotide sequence. The operable linkage to the vector may be producedusing a genetic recombination technology known in the art, and thesite-specific DNA cleavage and linkage may be produced using restrictionenzymes and ligases known in the art.

As used herein, the term “vector” refers to any mediator for cloningand/or transferring of bases into an organism, such as a host cell. Thevector may be a replicon that is able to bring the replication ofcombined fragments in which different DNA fragments are combined.Herein, the term “replicon” refers to any genetic unit (e.g., plasmid,phage, cosmid, chromosome, virus) which functions as a self-unit of DNAreplication in vivo, i.e., which is able to be replicated byself-regulation. As used herein, the term “vector” may comprise viraland non-viral mediators for introducing the bases into the organism,e.g., a host cell, in vitro, ex vivo, or in vivo, and may also comprisea minicircular DNA, a transposon such as Sleeping Beauty (Izsvak et al.J. Mol. Biol. 302:93-102 (2000)), or an artificial chromosome. Examplesof the vector commonly used may include natural or recombinant plasmids,cosmids, viruses, and bacteriophages. For example, as a phage vector orcosmid vector, pWE15, M13, MBL3, MBL4, IXII, ASHII, APII, t10, t11,Charon4A, and Charon21A, etc., may be used; and as a plasmid vector,those based on pBR, pUC, pBluescriptII, pGEM, pTZ, pCL, and pET, etc.,may be used. The vectors that may be used in the present disclosure arenot particularly limited, but any known expression vector may be used.Further, the vector may be a recombinant vector characterized by furthercomprising various antibiotic resistance genes. As used herein, the term“antibiotic resistance gene” refers to a gene having resistance againstan antibiotic, and a cell having this gene survives in an environmenttreated with the corresponding antibiotic. Therefore, the antibioticresistance gene is used as a selectable marker during production of alarge amount of plasmids in Escherichia.coli. The antibiotic resistancegene in the present disclosure is not a factor that greatly influencesexpression efficiency according to optimal combinations of vectors whichis a key technology of the present disclosure, and thus an antibioticresistance gene that is generally used as a selectable marker may beused without limitation. Specific examples may include a resistance geneagainst ampicilin, tetracyclin, kanamycin, chloroamphenicol,streptomycin, or neomycin, etc.

The microorganism expressing the fructose-6-phosphate-4-epimerase whichmay be used in the present disclosure may be obtained by a method ofintroducing the vector comprising the nucleic acid encoding the enzymeinto a host cell, and a method of transforming the vector may be anymethod as long as it is able to introduce the nucleic acid into thecell. An appropriate standard technique known in the art may be selectedand performed. Electroporation, calcium phosphate co-precipitation,retroviral infection, microinjection, a DEAE-dextran method, a cationicliposome method, and a heat shock method may be included, but is notlimited thereto.

As long as the transformed gene may be expressed in the host cell, itmay be inserted into the chromosome of the host cell, or it may existextrachromosomally. Further, the gene comprises DNA and RNA as apolynucleotide encoding a polypeptide, and any form may be used withoutlimitation, as long as it may be introduced into the host cell andexpressed therein. For example, the gene may be introduced into the hostcell in the form of an expression cassette, which is a polynucleotideconstruct comprising all elements required for its autonomousexpression. Commonly, the expression cassette may comprise a promoteroperably linked to the gene, transcriptional termination signals,ribosome binding sites, and translation termination signals. Theexpression cassette may be in the form of a self-replicable expressionvector. In addition, the gene as it is or in the form of apolynucleotide construct may be introduced into the host cell andoperably linked to sequences required for expression in the host cell.

The microorganism of the present disclosure may include either aprokaryotic microorganism or a eukaryotic microorganism, as long as itis a microorganism capable of producing thefructose-6-phosphate-4-epimerase of the present disclosure by comprisingthe nucleic acid of the present disclosure or the recombinant vector ofthe present disclosure. For example, the microorganism may includemicroorganism strains belonging to the genus Escherichia, the genusErwinia, the genus Serratia, the genus Providencia, the genusCorynebacterium, and the genus Brevibacterium, and specifically, it maybe Escherichia.coli or Corynebacterium glutamicum, but is not limitedthereto. Specific examples of the microorganism may includeEscherichia.coli BL21(DE3)/CJ_KO_F6P4E, Escherichia.coliBL21(DE3)/CJ_RM_F6P4E, Escherichia.coli BL21(DE3)/CJ_RP_F6P4E,Escherichia.coli BL21(DE3)/CJ_LP_F6P4E, Escherichia.coliBL21(DE3)/pBT7-C-His-CJ_td1, etc.

The microorganism of the present disclosure may include anymicroorganism capable of expressing the fructose-6-phosphate-4-epimeraseof the present disclosure or related enzymes according to various knownmethods, in addition to introduction of the nucleic acid or the vector.

The culture of the microorganism of the present disclosure may beproduced by culturing, in a medium, the microorganism capable ofexpressing the tagatose-bisphosphate aldolase of the present disclosureor related enzymes.

As used herein, the term “culturing” means that the microorganism isallowed to grow under appropriately controlled environmental conditions.The culturing process of the present disclosure may be carried outaccording to an appropriate medium and culture conditions known in theart. The culturing process may be easily adjusted by those skilled inthe art according to the strain to be selected. The step of culturingthe microorganism may be, but is not particularly limited to, carriedout by a batch process, a continuous process, or a fed batch processetc. With regard to the culture conditions, a proper pH (e.g., pH 5 to9, specifically pH 7 to 9) may be adjusted using a basic compound (e.g.,sodium hydroxide, potassium hydroxide, or ammonia) or an acidic compound(e.g., phosphoric acid or sulfuric acid), but is not particularlylimited thereto. Additionally, an antifoaming agent such as fatty acidpolyglycol ester may be added during the culturing process to preventfoam generation. Additionally, oxygen or an oxygen-containing gas may beinjected into the culture in order to maintain an aerobic state of theculture; or nitrogen, hydrogen, or carbon dioxide gas may be injectedwithout the injection of a gas in order to maintain an anaerobic ormicroaerobic state of the culture. The culture temperature may bemaintained from 25° C. to 40° C., and specifically, from 30° C. to 37°C., but is not limited thereto. The culturing may be continued until thedesired amount of useful materials is obtained, and specifically forabout 0.5 hours to about 60 hours, but is not limited thereto.Furthermore, the culture medium to be used may comprise, as carbonsources, sugars and carbohydrates (e.g., glucose, sucrose, lactose,fructose, maltose, molasses, starch, and cellulose), oils and fats(e.g., soybean oil, sunflower oil, peanut oil, and coconut oil), fattyacids (e.g., palmitic acid, stearic acid, and linoleic acid), alcohols(e.g., glycerol and ethanol), and organic acids (e.g., acetic acid) etc.These substances may be used individually or in a mixture, but are notlimited thereto. Nitrogen sources may include nitrogen-containingorganic compounds (e.g., peptone, yeast extract, meat extract, maltextract, corn steep liquor, soybean meal, and urea) or inorganiccompounds (e.g., ammonium sulfate, ammonium chloride, ammoniumphosphate, ammonium carbonate, and ammonium nitrate) etc. These nitrogensources may also be used individually or in a mixture, but are notlimited thereto. Phosphorus sources may include potassium dihydrogenphosphate, dipotassium hydrogen phosphate, or the correspondingsodium-containing salts etc. These nitrogen sources may also be usedindividually or in a mixture, but are not limited thereto. The culturemedium may comprise essential growth stimulators, such as metal salts(e.g., magnesium sulfate or iron sulfate), amino acids, and vitamins.

Another aspect of the present disclosure provides a composition forproducing tagatose, comprising tagatose-bisphosphate aldolase, amicroorganism expressing the tagatose-bisphosphate aldolase, or aculture of the microorganism; and tagatose-6-phosphate phosphatase, themicroorganism expressing the tagatose-6-phosphate phosphatase, or aculture of the microorganism.

The description of the composition for producing tagatose-6-phosphatemay be also applied to the composition for producing tagatose. Thetagatose-6-phosphate phosphatase of the present disclosure may be anyprotein without limitation, as long as it has activity to converttagatose-6-phosphate into tagatose by eliminating a phosphate group ofthe tagatose-6-phosphate. The tagatose-6-phosphate phosphatase of thepresent disclosure may be an enzyme derived from a heat-resistantmicroorganism, for example, an enzyme derived from Thermotoga sp. or avariant thereof, specifically, an enzyme derived from Thermotogamaritima or a variant thereof.

According to one embodiment of the present disclosure, thetagatose-6-phosphate phosphatase of the present disclosure may be aprotein which consists of an amino acid sequence of SEQ ID NO: 11, asequence having a genetic homology of 70%, 75%, 80%, 85%, 90%, 95%, 97%,99%, or 100% thereto, or a genetic homology within the range determinedby any two values of the above values. According to one embodiment ofthe present disclosure, the tagatose-6-phosphate phosphatase consistingof the amino acid sequence of SEQ ID NO: 11 of the present disclosuremay be encoded by a nucleotide sequence of SEQ ID NO: 12.

The composition for producing tagatose of the present disclosure mayfurther comprise glucose-6-phosphate isomerase, a microorganismexpressing the glucose-6-phosphate isomerase, or a culture of themicroorganism. In the presence of the enzyme, glucose-6-phosphate may beisomerized to produce fructose-6-phosphate. Theglucose-6-phosphate-isomerase of the present disclosure may include anyprotein without limitation, as long as it has activity to isomerizeglucose-6-phosphate into fructose-6-phosphate. Theglucose-6-phosphate-isomerase of the present disclosure may be an enzymederived from a heat-resistant microorganism, for example, an enzymederived from Thermotoga sp. or a variant thereof, specifically, anenzyme derived from Thermotoga maritima or a variant thereof. Accordingto one embodiment of the present disclosure, theglucose-6-phosphate-isomerase of the present disclosure may be a proteinwhich consists of an amino acid sequence of SEQ ID NO: 13, a sequencehaving a genetic homology of 70%, 75%, 80%, 85%, 90%, 95%, 97%, 99%, or100% thereto, or a homology within the range determined by any twovalues of the above values. According to one embodiment of the presentdisclosure, the glucose-6-phosphate-isomerase consisting of the aminoacid sequence of SEQ ID NO: 13 of the present disclosure may be encodedby a nucleotide sequence of SEQ ID NO: 14.

The composition for producing tagatose of the present disclosure mayfurther comprise phosphoglucomutase, a microorganism expressing thephosphoglucomutase, or a culture of the microorganism. The enzymecatalyzes a reversible reaction of converting glucose-1-phosphate intoglucose-6-phosphate or converting glucose-6-phosphate intoglucose-1-phosphate. The phosphoglucomutase of the present disclosuremay include any protein without limitation, as long as it has activityto convert glucose-1-phosphate into glucose-6-phosphate or to convertglucose-6-phosphate into glucose-1-phosphate. The phosphoglucomutase ofthe present disclosure may be an enzyme derived from a heat-resistantmicroorganism, for example, an enzyme derived from Thermotoga sp. or avariant thereof, specifically, an enzyme derived from Thermotoganeapolitana or a variant thereof. According to one embodiment of thepresent disclosure, the phosphoglucomutase of the present disclosure maybe a protein which consists of an amino acid sequence of SEQ ID NO: 15,a sequence having a genetic homology of 70%, 75%, 80%, 85%, 90%, 95%,97%, 99%, or 100% thereto, or within the range determined by any twovalues of the above values. According to one embodiment of the presentdisclosure, the phosphoglucomutase consisting of the amino acid sequenceof SEQ ID NO: 15 of the present disclosure may be encoded by anucleotide sequence of SEQ ID NO: 16.

The composition for producing tagatose of the present disclosure mayfurther comprise glucokinase, a microorganism expressing theglucokinase, or a culture of the microorganism. The glucokinase of thepresent disclosure may include any protein without limitation, as longas it has activity to phosphorylate glucose. The glucokinase of thepresent disclosure may be an enzyme derived from a heat-resistantmicroorganism, for example, an enzyme derived from Deinococcus sp. orAnaerolinea sp., or a variant thereof, specifically, an enzyme derivedfrom Deinococcus geothermalis or Anaerolinea thermophila, or a variantthereof. The glucokinase of the present disclosure may include anyprotein without limitation, as long as it has activity to convertglucose into glucose-6-phosphate. Specifically, the glucokinase of thepresent disclosure may be a phosphate-dependent glucokinase. Accordingto one embodiment of the present disclosure, the glucokinase of thepresent disclosure may be a protein which consists of an amino acidsequence of SEQ ID NO: 17 or 19, a sequence having a genetic homology of70%, 75%, 80%, 85%, 90%, 95%, 97%, 99%, or 100% thereto, or a genetichomology within the range determined by any two values of the abovevalues. According to one embodiment of the present disclosure, theglucokinase consisting of the amino acid sequence of SEQ ID NO: 17 ofthe present disclosure may be encoded by a nucleotide sequence of SEQ IDNO: 18, and the glucokinase consisting of the amino acid sequence of SEQID NO: 19 of the present disclosure may be encoded by a nucleotidesequence of SEQ ID NO: 20.

The composition for producing tagatose of the present disclosure mayfurther comprise α-glucan phosphorylase, starch phosphorylase,maltodextrin phosphorylase, or sucrose phosphorylase, a microorganismexpressing the same, or a culture of the microorganism. Thephosphorylase may include any protein without limitation, as long as ithas activity to convert starch, maltodextrin, or sucrose intoglucose-1-phosphate. The phosphorylase may be an enzyme derived from aheat-resistant microorganism, for example, an enzyme derived fromThermotoga sp. or a variant thereof, specifically, an enzyme derivedfrom Thermotoga neapolitana or a variant thereof. The phosphorylase ofthe present disclosure may be a protein which consists of an amino acidsequence of SEQ ID NO: 21, a sequence having a genetic homology of 70%,75%, 80%, 85%, 90%, 95%, 97%, 99%, or 100% thereto, or a genetichomology within the range determined by any two values of the abovevalues. According to one embodiment of the present disclosure, thephosphorylase consisting of the amino acid sequence of SEQ ID NO: 21 ofthe present disclosure may be encoded by a nucleotide sequence of SEQ IDNO: 22.

The composition for producing tagatose of the present disclosure mayfurther comprise α-amylase, pullulanase, glucoamylase, sucrase, orisoamylase; a microorganism expressing the amylase, pullulanase,glucoamylase, sucrase, or isoamylase; or a culture of the microorganismexpressing the amylase, pullulanase, glucoamylase, sucrase, orisoamylase.

The composition for producing tagatose of the present disclosure maycomprise two or more enzymes of the above-described enzymes which may beused in the production of tagatose or transformants thereofindividually, or a transformant transformed with nucleotides encodingthe two or more enzymes.

The composition for producing tagatose of the present disclosure mayfurther comprise 4-α-glucanotransferase, a microorganism expressing the4-α-glucanotransferase, or a culture of the microorganism expressing the4-α-glucanotransferase. The 4-α-glucanotransferase of the presentdisclosure may include any protein without limitation, as long as it hasactivity to convert glucose into starch, maltodextrin, or sucrose. The4-α-glucanotransferase of the present disclosure may be an enzymederived from a heat-resistant microorganism, for example, an enzymederived from Thermotoga sp. or a variant thereof, specifically, anenzyme derived from Thermotoga maritime or a variant thereof. Accordingto one embodiment of the present disclosure, the 4-α-glucanotransferaseof the present disclosure may be a protein which consists of an aminoacid sequence of SEQ ID NO: 23, a sequence having a genetic homology of70%, 75%, 80%, 85%, 90%, 95%, 97%, 99%, or 100% thereto, or a genetichomology within the range determined by any two values of the abovevalues. According to one embodiment of the present disclosure, the4-α-glucanotransferase consisting of the amino acid sequence of SEQ IDNO: 23 of the present disclosure may be encoded by a nucleotide sequenceof SEQ ID NO: 24.

Examples of the microorganisms which may be used in the above-describedembodiments may include Escherichia.coli BL21(DE3)/pET21a-CJ_ct1,Escherichia.coli BL21(DE3)/pET21a-CJ_ct2, Escherichia.coliBL21(DE3)/pET21a-CJ_tn1, Escherichia.coli BL21(DE3)/pET21a-CJ_tn2, andEscherichia.coli BL21(DE3)/pET21a-CJ_t4, etc. The recombinantmicroorganisms were deposited at Korean Culture Center of Microorganismson Mar. 20, 2017 with Accession Nos. KCCM11990P (Escherichia.coliBL21(DE3)/pET21a-CJ_ct1), KCCM11991P (Escherichia.coliBL21(DE3)/pET21a-CJ_ct2), KCCM11992P (Escherichia.coliBL21(DE3)/pET21a-CJ_tn1), KCCM11993P (Escherichia.coliBL21(DE3)/pET21a-CJ_tn2), KCCM11994P (Escherichia.coliBL21(DE3)/pET21a-CJ_t4), respectively.

The composition for producing tagatose of the present disclosure mayfurther comprise a substance, a component, or a compositioncorresponding to a substrate of each of the above-described enzymes.

The composition for producing tagatose of the present disclosure mayfurther comprise any suitable excipient commonly used in thecorresponding composition for producing tagatose. The excipient mayinclude, for example, a preservative, a wetting agent, a dispersingagent, a suspending agent, a buffer, a stabilizing agent, or an isotonicagent, etc., but is not limited thereto.

The composition for producing tagatose of the present disclosure mayfurther comprise a metal. In one embodiment, the metal of the presentdisclosure may be a metal containing a divalent cation. Specifically,the metal of the present disclosure may be nickel, cobalt, aluminum,magnesium (Mg), or manganese (Mn). More specifically, the metal of thepresent disclosure may be a metal ion or a metal salt, and much morespecifically, the metal salt may be NiSO₄, MgSO₄, MgCl₂, NiCl₂, CoCl₂,CoSO₄, MnCl₂, or MnSO₄.

Another aspect of the present disclosure relates to a method ofproducing tagatose-6-phosphate, comprising convertingfructose-6-phosphate into tagatose-6-phosphate by contactingfructose-6-phosphate with tagatose-bisphosphate aldolase, themicroorganism expressing the tagatose-bisphosphate aldolase, or theculture of the microorganism.

The description of the composition for producing tagatose-6-phosphatemay be also applied to the composition for producing tagatose.

Another aspect of the present disclosure relates to a method ofproducing tagatose, comprising converting fructose-6-phosphate intotagatose-6-phosphate by contacting fructose-6-phosphate withtagatose-bisphosphate aldolase, the microorganism expressing thetagatose-bisphosphate aldolase, or the culture of the microorganism. Themethod of producing tagatose may further comprise convertingtagatose-6-phosphate into tagatose by contacting tagatose-6-phosphatewith tagatose-6-phosphate phosphatase, the microorganism expressing thetagatose-6-phosphate phosphatase, or the culture of the microorganism.

The method of the present disclosure may further comprise convertingglucose-6-phosphate into fructose-6-phosphate by contactingglucose-6-phosphate with the glucose-6-phosphate-isomerase of thepresent disclosure, the microorganism expressing theglucose-6-phosphate-isomerase, or the culture of the microorganismexpressing the glucose-6-phosphate-isomerase.

The method of the present disclosure may further comprise convertingglucose-1-phosphate into glucose-6-phosphate by contactingglucose-1-phosphate with the phosphoglucomutase of the presentdisclosure, the microorganism expressing the phosphoglucomutase, or theculture of the microorganism expressing the phosphoglucomutase.

The method of the present disclosure may further comprise convertingglucose into glucose-6-phosphate by contacting glucose with theglucokinase of the present disclosure, the microorganism expressing theglucokinase, or the culture of the microorganism expressing theglucokinase.

The method of the present disclosure may further comprise convertingstarch, maltodextrin, or sucrose into glucose-1-phosphate by contactingstarch, maltodextrin, sucrose, or a combination thereof with theα-glucan phosphorylase, starch phosphorylase, maltodextrinphosphorylase, or sucrose phosphorylase of the present disclosure, themicroorganism expressing the phosphorylase, or the culture of themicroorganism expressing the phosphorylase.

The method of the present disclosure may further comprise convertingstarch, maltodextrin, or sucrose into glucose by contacting starch,maltodextrin, sucrose, or a combination thereof with the α-amylase,pullulanase, glucoamylase, sucrase, or isoamylase; the microorganismexpressing the α-amylase, pullulanase, glucoamylase, sucrase, orisoamylase; or the culture of the microorganism expressing theα-amylase, pullulanase, glucoamylase, sucrase, or isoamylase.

The method of the present disclosure may further comprise convertingglucose into starch, maltodextrin, or sucrose by contacting glucose withthe 4-α-glucanotransferase of the present disclosure, the microorganismexpressing the 4-α-glucanotransferase, or the culture of themicroorganism expressing the 4-α-glucanotransferase.

Each contacting in the method of the present disclosure may be performedunder conditions of pH 5.0 to pH 9.0, 30° C. to 80° C., and/or for 0.5hours to 48 hours. Specifically, the contacting of the presentdisclosure may be performed under a condition of pH 6.0 to pH 9.0 or pH7.0 to pH 9.0. Further, the contacting of the present disclosure may beperformed under a temperature condition of 35° C. to 80° C., 40° C. to80° C., 45° C. to 80° C., 50° C. to 80° C., 55° C. to 80° C., 60° C. to80° C., 30° C. to 70° C., 35° C. to 70° C., 40° C. to 70° C., 45° C. to70° C., 50° C. to 70° C., 55° C. to 70° C., 60° C. to 70° C., 30° C. to65° C., 35° C. to 65° C., 40° C. to 65° C., 45° C. to 65° C., 50° C. to65° C., 55° C. to 65° C., 30° C. to 60° C., 35° C. to 60° C., 40° C. to60° C., 45° C. to 60° C., 50° C. to 60° C. or 55° C. to 60° C.Furthermore, the contacting of the present disclosure may be performedfor 0.5 hours to 36 hours, 0.5 hours to 24 hours, 0.5 hours to 12 hours,0.5 hours to 6 hours, 1 hour to 36 hours, 1 hour to 24 hours, 1 hour to12 hours, 1 hour to 6 hours, 3 hours to 36 hours, 3 hours to 24 hours, 3hours to 12 hours, 3 hours to 6 hours, 12 hours to 36 hours, or 18 hoursto 30 hours.

In one embodiment, the contacting of the present disclosure may beperformed in the presence of a metal, a metal ion, or a metal salt.

Another aspect of the present disclosure relates to a method ofproducing tagatose, comprising contacting the composition for producingtagatose described herein with starch, maltodextrin, sucrose, or acombination thereof; and phosphate.

In a specific embodiment of the present disclosure, a method ofproducing tagatose is provided, comprising:

-   -   converting glucose into glucose-6-phosphate by contacting        glucose with the glucokinase of the present disclosure, the        microorganism expressing the glucokinase, or the culture of the        microorganism,    -   converting glucose-6-phosphate into fructose-6-phosphate by        contacting glucose-6-phosphate with the        glucose-6-phosphate-isomerase of the present disclosure, the        microorganism expressing the glucose-6-phosphate-isomerase, or        the culture of the microorganism,    -   converting fructose-6-phosphate into tagatose-6-phosphate by        contacting fructose-6-phosphate with the        fructose-6-phosphate-4-epimerase of the present disclosure, the        microorganism expressing the fructose-6-phosphate-4-epimerase,        or the culture of the microorganism, and    -   converting tagatose-6-phosphate into tagatose by contacting        tagatose-6-phosphate with the tagatose-6-phosphate phosphatase        of the present disclosure, the microorganism expressing the        tagatose-6-phosphate phosphatase, or the culture of the        microorganism.

The conversion reactions may be performed sequentially or in situ in thesame reaction system. In the method, phosphate released fromtagatose-6-phosphate by phosphatase may be used as a substrate of theglucokinase to produce glucose-6-phosphate. Therefore, phosphate is notaccumulated, and as a result, a high conversion rate may be obtained.

In the method, glucose may be, for example, produced by convertingstarch, maltodextrin, or sucrose into glucose by contacting starch,maltodextrin, sucrose, or a combination thereof with α-glucanphosphorylase, starch phosphorylase, maltodextrin phosphorylase, sucrosephosphorylase of the present disclosure, the microorganism expressingthe phosphorylase, or the culture of the microorganism expressing thephosphorylase. Therefore, the method according to a specific embodimentmay further comprise converting starch, maltodextrin, or sucrose intoglucose.

In another specific embodiment of the present disclosure, a method ofproducing tagatose is provided, comprising:

-   -   converting glucose-1-phosphate into glucose-6-phosphate by        contacting glucose-1-phosphate with the phosphoglucomutase of        the present disclosure, the microorganism expressing the        phosphoglucomutase, or the culture of the microorganism,    -   converting glucose-6-phosphate into fructose-6-phosphate by        contacting glucose-6-phosphate with the        glucose-6-phosphate-isomerase of the present disclosure, the        microorganism expressing the glucose-6-phosphate-isomerase, or        the culture of the microorganism,    -   converting fructose-6-phosphate into tagatose-6-phosphate by        contacting fructose-6-phosphate with the        fructose-6-phosphate-4-epimerase of the present disclosure, the        microorganism expressing the fructose-6-phosphate-4-epimerase,        or the culture of the microorganism, and    -   converting tagatose-6-phosphate into tagatose by contacting        tagatose-6-phosphate with the tagatose-6-phosphate phosphatase        of the present disclosure, the microorganism expressing the        tagatose-6-phosphate phosphatase, or the culture of the        microorganism.

The conversion reactions may be performed sequentially or in situ in thesame reaction system.

In the method, glucose-1-phosphate may be, for example, produced byconverting starch, maltodextrin, or sucrose into glucose-1-phosphate bycontacting starch, maltodextrin, sucrose, or a combination thereof withα-glucan phosphorylase, starch phosphorylase, maltodextrinphosphorylase, sucrose phosphorylase of the present disclosure, themicroorganism expressing the phosphorylase, or the culture of themicroorganism expressing the phosphorylase. Therefore, the methodaccording to a specific embodiment may further comprise convertingstarch, maltodextrin, or sucrose into glucose-1-phosphate. In thisregard, phosphate released from tagatose-6-phosphate by phosphatase maybe used as a substrate of the phosphorylase to produceglucose-1-phosphate. Therefore, phosphate is not accumulated, and as aresult, a high conversion rate may be obtained.

The method may further comprise purifying the produced tagatose. Thepurification in the method is not particularly limited, and a methodcommonly used in the art to which the present disclosure pertains may beused. Non-limiting examples may include chromatography, fractionalcrystallization, and ion purification, etc. The purification method maybe performed only by a single method or by two or more methods. Forexample, the tagatose product may be purified through chromatography,and separation of the sugar by the chromatography may be performed byutilizing a difference in a weak binding force between the sugar to beseparated and a metal ion attached to an ion resin.

In addition, the present disclosure may further comprise performingdecolorization, desalination, or both of decolorization and desalinationbefore or after the purification step of the present disclosure. Byperforming the decolorization and/or desalination, it is possible toobtain a more purified tagatose product without impurities.

Hereinafter, the present disclosure will be described in more detailwith reference to Examples. However, these Examples are provided forbetter understanding, and the disclosure is not intended to be limitedby these Examples.

Example 1: Production of Recombinant Expression Vector and Transformantof Each Enzyme

To provide α-glucan phosphorylase, phosphoglucomutase,glucose-6-phosphate-isomerase, 4-α-glucanotransferase which areheat-resistant enzymes needed in the production pathway of tagatose ofthe present disclosure, nucleotide sequences expected as the enzymes[the above enzymes are represented by SEQ ID NO: 22(CT1), SEQ ID NO:16(CT2), SEQ ID NO: 14(TN1), and SEQ ID NO: 24(TN2), respectively] wereselected from a nucleotide sequence of a thermophilic microorganism,Thermotoga neapolitana or Thermotoga maritima, which is registered inGenbank.

Based on the selected nucleotide sequences, forward primers (SEQ ID NO:21: CT1-Fp, SEQ ID NO: 27: CT2-Fp, SEQ ID NO: 29: TN1-Fp, SEQ ID NO: 31:TN2-Fp) and reverse primers (SEQ ID NO: 26: CT1-Rp, SEQ ID NO: 28:CT2-Rp, SEQ ID NO: 30: TN1-Rp, SEQ ID NO: 32: TN2-Rp) were designed andsynthesized, and the gene of each enzyme was amplified by PCR using theabove primers and a genomic DNA of the Thermotoga neapolitana as atemplate. Each amplified gene of the enzymes was inserted into pET21a(Novagen) which is a plasmid vector for expression in Escherichia.coliusing restriction enzymes, NdeI and XhoI or SalI, thereby producingrecombinant expression vectors designated as pET21a-CJ_ct1,pET21a-CJ_ct2, pET21a-CJ_tn1, pET21a-CJ_tn2, respectively.

Each of the expression vectors was transformed into Escherichia.coliBL21(DE3) according to a common transformation method [see Sambrook etal. 1989], thereby producing transformants (transformed microorganisms)designated as Escherichia.coli BL21(DE3)/pET21a-CJ_ct1, Escherichia.coliBL21(DE3)/pET21a-CJ_ct2, Escherichia.coli BL21(DE3)/pET21a-CJ_tn1,Escherichia.coli BL21(DE3)/pET21a-CJ_tn2, respectively. Thesetransformants were deposited at the Korean Culture Center ofMicroorganisms under the provisions of the Budapest Treaty on Mar. 20,2017 with Accession Nos. KCCM11990P (Escherichia.coliBL21(DE3)/pET21a-CJ_ct1), KCCM11991P (Escherichia.coliBL21(DE3)/pET21a-CJ_ct2), KCCM11992P (Escherichia.coliBL21(DE3)/pET21a-CJ_tn1), and KCCM11993P (Escherichia.coliBL21(DE3)/pET21a-CJ_tn2), respectively.

Example 2: Production of Recombinant Enzymes

Escherichia.coli BL21(DE3)/pET21a-CJ_ct1, Escherichia.coliBL21(DE3)/pET21a-CJ_ct2, Escherichia.coli BL21(DE3)/pET21a-CJ_tn1,Escherichia.coli BL21(DE3)/pET21a-CJ_tn2 expressing each of the enzymesproduced in Example 1 were seeded in a culture tube containing 5 ml ofLB liquid medium, and then seed culture was performed in a shakingincubator at 37° C. until absorbance at 600 nm reached 2.0.

Each of the cultures obtained by the seed culture was seeded in aculture flask containing an LB liquid medium, and then main culture wasperformed. When absorbance at 600 nm reached 2.0, 1 mM IPTG was added toinduce expression and production of the recombinant enzymes. During theculture, a shaking speed was maintained at 180 rpm and a culturetemperature was maintained at 37° C. Each culture was centrifuged at8,000×g and 4° C. for 20 minutes to recover cells. The recovered cellswere washed with 50 mM Tris-HCl (pH 8.0) buffer twice and suspended inthe same buffer, followed by cell disruption using a sonicator. Celllysates were centrifuged at 13,000×g and 4° C. for 20 minutes to obtainonly supernatants. Each enzyme was purified therefrom using His-tagaffinity chromatography. The purified recombinant enzyme solution wasdialyzed against 50 mM Tris-HCl (pH 8.0) buffer, and used for reaction.

A molecular weight of each purified enzyme was examined by SDS-PAGE, andas a result, it was confirmed that CT1 (α-glucan phosphorylase) has amolecular weight of about 96 kDa, CT2 (phosphoglucomutase) has amolecular weight of about 53 kDa, TN1 (glucose-6-phosphate-isomerase)has a molecular weight of about 51 kDa.

Example 3: Examination of Fructose-6-Phosphate-4-Epimerase Activity ofTagatose-Bisphosphate Aldolase

3-1. Production of Recombinant Expression Vector and RecombinantMicroorganism Comprising Tagatose-Bisphosphate Aldolase Gene

To identify a novel heat-resistant fructose-6-phosphate-4-epimerase,genetic information of tagatose-bisphosphate aldolase derived fromKosmotoga olearia, Rhodothermus marinus, Rhodothermus profundi, andLimnochorda pilosa which are thermophilic microorganisms was acquired toproduce recombinant vectors expressible in Escherichia.coli andrecombinant microorganisms.

In detail, a nucleotide sequence of tagatose-bisphosphate aldolase wasselected from nucleotide sequences of Kosmotoga olearia or Rhodothermusmarinus ATCC 43812, Rhodothermus profundi DSM 22212, and Limnochordapilosa DSM 28787, which are registered in Genbank and KEGG (KyotoEncyclopedia of Genes and Genomes), and based on information of aminoacid sequences (SEQ ID NOS: 1, 3, 5 and 7) and nucleotide sequences (SEQID NOS: 2, 4, 6 and 8) of the four microorganisms,pBT7-C-His-CJ_KO_F6P4E, pBT7-C-His-CJ_RM_F6P4E, pBT7-C-His-CJ_RP_F6P4E,and pBT7-C-His-CJ_LP_F6P4E which are recombinant vectors comprising thenucleotide sequence of the enzyme and being expressible inEscherichia.coli were produced (Bioneer Corp., Korea).

Each of the produced expression vectors was transformed intoEscherichia.coli BL21(DE3) by heat shock transformation (Sambrook andRussell: Molecular cloning, 2001) to produce recombinant microorganisms,and used after being frozen and stored in 50% glycerol. The recombinantmicroorganisms were designated as Escherichia.coliBL21(DE3)/CJ_KO_F6P4E, Escherichia.coli BL21(DE3)/CJ_RM_F6P4E,Escherichia.coli BL21(DE3)/CJ_RP_F6P4E, and Escherichia.coliBL21(DE3)/CJ_LP_F6P4E, respectively and deposited at the Korean CultureCenter of Microorganisms (KCCM) which is an International DepositaryAuthority under the provisions of the Budapest Treaty with AccessionNos. KCCM11999P (date of deposit: Mar. 24, 2017), KCCM12096P (date ofdeposit: Aug. 11, 2017), KCCM12097P (date of deposit: Aug. 11, 2017),and KCCM12095P (date of deposit: Aug. 11, 2017), respectively.

To identify an additional novel heat-resistantfructose-6-phosphate-4-epimerase, a nucleotide sequence expected as theenzyme was selected from a nucleotide sequence of a thermophilicThermanaerothrix daxensis, which is registered in Genbank, and based oninformation of an amino acid sequence (SEQ ID NO: 9) and a nucleotidesequence (SEQ ID NO: 10) of the microorganism, the gene was insertedinto pBT7-C-His (Bioneer Corp.) which is a recombinant vector comprisingthe nucleotide sequence of the enzyme and being expressible inEscherichia.coli to produce a recombinant expression vector designatedas pBT7-C-His-CJ_td1. The expression vector was transformed into anEscherichia.coli BL21(DE3) strain by a common transformation method [seeSambrook et al. 1989] to produce a transformant (transformedmicroorganism) designated as Escherichia.coliBL21(DE3)/pBT7-C-His-CJ_td1, and this transformant was deposited at theKorean Culture Center of Microorganisms (KCCM) under the provisions ofthe Budapest Treaty on Mar. 20, 2017 with Accession No. KCCM11995P(Escherichia.coli BL21(DE3)/pBT7-C-His-CJ_td1).

3-2. Production of Recombinant Tagatose-Bisphosphate Aldolase Enzyme

To produce recombinant enzymes, CJ_KO_F6P4E, CJ_RM_F6P4E, CJ_RP_F6P4E,CJ_LP_F6P4E, and CJ_TD1_F6P4E from the produced recombinantmicroorganisms, each of the recombinant microorganisms was seeded in aculture tube containing 5 ml of an LB liquid medium with ampicillinantibiotic, and then seed culture was performed in a shaking incubatorat 37° C. until absorbance at 600 nm reached 2.0. Each of the culturesobtained by the seed culture was seeded in a culture flask containing anLB liquid medium, and then main culture was performed. When absorbanceat 600 nm reached 2.0, 1 mM IPTG (isopropyl β-D-1-thiogalactopyranoside)was added to induce expression and production of the recombinant enzyme.The seed culture and the main culture were performed under conditions of180 rpm and 37° C. Each culture of the main culture was centrifuged at8,000×g and 4° C. for 20 minutes to recover cells. The recovered cellswere washed with 25 mM Tris-HCl (pH 7.0) buffer twice and suspended inthe same buffer, followed by cell disruption using a sonicator. Eachcell lysate was centrifuged at 13,000×g and 4° C. for 20 minutes to takeonly a supernatant. The supernatant was purified using His-taq affinitychromatography, and 10 column volumes of 50 mM NaH₂PO₄ (pH 8.0) buffercontaining 20 mM imidazole and 300 mM NaCl was applied to removenon-specifically bound proteins. Next, 50 mM NaH₂PO₄ (pH 8.0) buffercontaining 250 mM imidazole and 300 mM NaCl was further applied toperform elution and purification. Dialysis was performed using 25 mMTris-HCl (pH 7.0) buffer to obtain CJ_KO_F6P4E, CJ_RM_F6P4E,CJ_RP_F6P4E, CJ_LP_F6P4E, and CJ_TD1_F6P4E which are purified enzymesfor analysis of enzyme characterization.

3-3. Analysis of Fructose-6-Phosphate-4-Epimerase Activity ofRecombinant Tagatose-Bisphosphate Aldolase Enzyme

The fructose-6-phosphate-4-epimerase activities of the recombinanttagatose-bisphosphate aldolase enzymes obtained in Example 3-2 wereanalyzed. In detail, 1% by weight of fructose-6-phosphate as a substratewas suspended in 25 mM Tris-HCl (pH 7.0) buffer, and each 1 unit/ml ofthe purified CJ_KO_F6P4E, CJ_RM_F6P4E, CJ_RP_F6P4E, CJ_LP_F6P4E, andCJ_TD1_F6P4E was added thereto, and allowed to react at 60° C. for 1hour. To remove phosphate, 1 unit/ml of phosphatase (Alkalinephosphatase of NEB, Calf Intestinal) was added and allowed to react at37° C. for 1 hour. Reaction products were analyzed by HPLC, and HPLCanalysis was performed under conditions of using a SP0810(Shodex) columnand applying a mobile phase (water) at 80° C. and a flow rate of 1ml/min, and resultants were analyzed using a refractive index detector.

As a result, it was confirmed that all of CJ_KO_F6P4E, CJ_RM_F6P4E,CJ_RP_F6P4E, and CJ_LP_F6P4E have the activity to convertfructose-6-phosphate into tagatose-6-phosphate (FIGS. 1A to 1D).

It was also confirmed that CJ_TD1_F6P4E has activity to convertfructose-6-phosphate into tagatose-6-phosphate (FIG. 5 ).

Example 4: Identification of Tagatose-6-Phosphate Phosphatase(D-Tagatose-6-Phosphate Phosphatase)

To perform production of tagatose from fructose-6-phosphate bysimultaneous complex enzyme reactions in the tagatose production pathwayof the present disclosure, tagatose-6-phosphate phosphatase which isable to exert the simultaneous enzyme reaction together withtagatose-bisphosphate aldolase was identified.

4-1. Production of Recombinant Expression Vector and RecombinantMicroorganism Comprising Tagatose-6-Phosphate Phosphatase Gene

A nucleotide sequence (SEQ ID NO: 12, hereinafter, referred to as t4)and an amino acid sequence (SEQ ID NO: 11) expected as thetagatose-6-phosphate phosphatase were selected from a nucleotidesequence of Thermotoga maritima, which is registered in Genbank, andbased on the selected nucleotide sequence, a forward primer (SEQ ID NO:33) and a reverse primer (SEQ ID NO: 34) were designed and synthesized.Polymerase chain reaction (PCR) was performed using the primers andgenomic DNA of Thermotoga maritima as a template to amplify t4 gene. Theamplified gene was inserted into pET21a (Novagen) which is a plasmidvector for expression in Escherichia.coli using restriction enzymes NdeIand XhoI, thereby producing a recombinant expression vector which wasthen designated as pET21a-CJ_t4. The produced expression vector wastransformed into Escherichia.coli BL21(DE3) strain by heat shocktransformation (Sambrook and Russell: Molecular cloning, 2001) toproduce a recombinant microorganism, which was then used after beingfrozen and stored in 50% glycerol. The recombinant microorganism wasdesignated as Escherichia.coli BL21(DE3)/pET21a-CJ_t4, and deposited atthe Korean Culture Center of Microorganisms (KCCM) which is anInternational Depositary Authority under the provisions of the BudapestTreaty on Mar. 20, 2017 with Accession No. KCCM11994P.

4-2. Production of Recombinant Tagatose-6-Phosphate Phosphatase

Escherichia.coli BL21(DE3)/pET21a-CJ_t4 was seeded in a culture tubecontaining 5 ml of LB liquid medium and then seed culture was performedin a shaking incubator at 37° C. until absorbance at 600 nm reached 2.0.The culture obtained by the seed culture was seeded in a culture flaskcontaining an LB liquid medium, and then main culture was performed.When absorbance at 600 nm reached 2.0, 1 mM IPTG was added to induceexpression and production of the recombinant enzymes. The seed cultureand the main culture were performed at a shaking speed of 180 rpm and37° C. The culture obtained by the main culture was centrifuged at8,000×g and 4° C. for 20 minutes to recover cells. The recovered cellswere washed with 50 mM Tris-HCl (pH 8.0) buffer twice and suspended inthe same buffer, followed by cell disruption using a sonicator. A celllysate was centrifuged at 13,000×g and 4° C. for 20 minutes to obtainonly a supernatant. The enzyme was purified therefrom using His-tagaffinity chromatography. The purified enzyme was used after dialysisagainst 50 mM Tris-HCl (pH 8.0) buffer, and the purified recombinantenzyme was designated as CJ_T4.

4-3. Analysis of Tagatose-6-Phosphate Phosphatase Activity of CJ_T4

To analyze activity of CJ_T4, tagatose-6-phosphate was suspended in 50mM Tris-HCl (pH 7.5) buffer, and 0.1 unit/ml of the purified CJ_T4 and10 mM MgCl₂ were added thereto and allowed to react at 70° C. for 10minutes. Then, the reaction product was analyzed by HPLC. HPLC analysiswas performed under conditions of using a HPX-87H (Bio-Rad) column andapplying a mobile phase (water) at 60° C. and a flow rate of 0.6 ml/min,and tagatose and tagatose-6-phosphate were analyzed using a refractiveindex detector.

As a result, tagatose was produced in the reaction product. As a resultof performing the same reaction after adding CJ_T4 to phosphate andtagatose reactants, no tagatose was produced, indicating that CJ_T4 hasirreversible tagatose-6-phosphate phosphatase activity (FIG. 3 ).

Example 5: Production of Tagatose by Simultaneous Complex EnzymeReactions

1% (w/v) fructose-6-phosphate suspended in 25 mM Tris-HCl (pH 7.0)buffer was added to a mixed enzyme solution of 1 unit/ml of CJ_KO_F6P4Eor CJ_RP_F6P4E and 1 unit/ml of CJ_t4 (Accession No. KCCM11994P), andallowed to react at 60° C. for 1 hour, and then HPLC was performed toanalyze the reaction product. HPLC analysis was performed underconditions of using a SP0810 (Shodex) column and applying a mobile phase(water) at 80° C. and a flow rate of 1 ml/min, and tagatose was detectedusing a refractive index detector.

As a result, tagatose production was observed, indicating that tagatosemay be produced from fructose-6-phosphate by simultaneous complex enzymereactions of tagatose-bisphosphate aldolase and tagatose-6-phosphatephosphatase (FIGS. 2A and 2B).

Example 6: Production of Tagatose from Maltodextrin by SimultaneousComplex Enzyme Reactions

To analyze the activity to produce tagatose from maltodextrin by complexenzymes, 5% (w/v) maltodextrin was added to a reaction solutioncontaining 1 unit/ml of CT1, 1 unit/ml of CT2, 1 unit/ml of TN1, 1unit/ml of T4, 1 unit/ml of TD1, 20 mM to 50 mM of sodium phosphate (pH7.0), and allowed to react at 60° C. for 1 hour, and then HPLC wasperformed to analyze the reaction product. HPLC analysis was performedunder conditions of using a SP0810 (Shodex) column and applying a mobilephase (water) at 80° C. and a flow rate of 0.6 ml/min, and tagatose wasdetected using a refractive index detector.

As a result, it was confirmed that tagatose may be produced frommaltodextrin by the complex enzyme reactions of added CT1, CT2, TN1, T4,and TD1 (FIG. 6 ).

Effect of the Invention

A method of producing tagatose according to the present disclosure iseconomical because of using glucose or starch as a raw material,accumulates no phosphate to achieve a high conversion rate, andcomprises a tagatose-6-phosphate phosphatase reaction which is anirreversible reaction pathway, thereby remarkably increasing aconversion rate into tagatose.

Further, tagatose may be produced from glucose or starch as a rawmaterial by complex enzyme reactions, and thus there are advantages thatthe method is simple and economical, and a yield is improved.

International Depositary Authority: Korean Culture Center ofMicroorganisms (foreign)

-   -   Accession No: KCCM11990P    -   Date of deposit: 2017 Mar. 20

International Depositary Authority: Korean Culture Center ofMicroorganisms (foreign)

-   -   Accession No: KCCM11991P    -   Date of deposit: 2017 Mar. 20

International Depositary Authority: Korean Culture Center ofMicroorganisms (foreign)

-   -   Accession No: KCCM11992P    -   Date of deposit: 2017 Mar. 20

International Depositary Authority: Korean Culture Center ofMicroorganisms (foreign)

-   -   Accession No: KCCM11993P    -   Date of deposit: 2017 Mar. 20

International Depositary Authority: Korean Culture Center ofMicroorganisms (foreign)

-   -   Accession No: KCCM11994P    -   Date of deposit: 2017 Mar. 20

International Depositary Authority: Korean Culture Center ofMicroorganisms (foreign)

-   -   Accession No: KCCM11995P    -   Date of deposit: 2017 Mar. 20

International Depositary Authority: Korean Culture Center ofMicroorganisms (foreign)

-   -   Accession No: KCCM11999P    -   Date of deposit: 2017 Mar. 24

International Depositary Authority: Korean Culture Center ofMicroorganisms (foreign)

-   -   Accession No: KCCM12096P    -   Date of deposit: 2017 Aug. 11

International Depositary Authority: Korean Culture Center ofMicroorganisms (foreign)

-   -   Accession No: KCCM12097P    -   Date of deposit: 2017 Aug. 11

International Depositary Authority: Korean Culture Center ofMicroorganisms (foreign)

-   -   Accession No: KCCM12095P    -   Date of deposit: 2017 Aug. 11

What is claimed is:
 1. A method of producing tagatose, comprising: (a)producing tagatose-6-phosphate by contacting fructose-6-phosphate withtagatose-6-phosphate kinase, a microorganism expressing thetagatose-6-phosphate kinase, or a culture of the microorganism, whereinthe tagatose-6-phosphate kinase consists of the amino acid sequence ofSEQ ID NO: 3 or 5; and (b) producing tagatose by contacting the producedtagatose-6-phosphate with tagatose-6-phosphatase, a microorganismexpressing the tagatose-6-phosphate phosphatase, or a culture of themicroorganism.
 2. The method of claim 1, further comprising convertingglucose-6-phosphate into fructose-6-phosphate by contactingglucose-6-phosphate with glucose-6-phosphate-isomerase, a microorganismexpressing the glucose-6-phosphate-isomerase, or a culture of themicroorganism.
 3. The method of claim 2, further comprising convertingglucose-1-phosphate into glucose-6-phosphate by contactingglucose-1-phosphate with phosphoglucomutase, a microorganism expressingthe phosphoglucomutase, or a culture of the microorganism.
 4. The methodof claim 3, further comprising converting, starch, maltodextrin, orsucrose into glucose-1-phosphate by contacting starch, maltodextrin,sucrose, or a combination thereof with α-glucan phosphorylase, starchphosphorylase, maltodextrin phosphorylase, or sucrose phosphorylase, amicroorganism expressing the α-glucan phosphorylase, starchphosphorylase, maltodextrin phosphorylase, or sucrose phosphorylase, ora culture of the microorganism.
 5. The method of claim 2, furthercomprising converting glucose into glucose-6-phosphate by contactingglucose with glucokinase, a microorganism expressing the glucokinase, ora culture of the microorganism.
 6. The method of claim 5, furthercomprising convening starch, maltodextrin or sucrose into glucose bycontacting starch, maltodextrin, sucrose, or a combination thereof withα-amylase, pullulanase, glucoamylase, sucrase, or isoamylase, amicroorganism expressing the α-amylase, pullulanase, glucoamylase,sucrose, or isoamylase, or a culture of the microorganism.
 7. The methodof claim 1, wherein the contacting is performed at pH 5.0 to 9.0, 40° C.to 80° C., or for 0.5 hours to 24 hours.
 8. A method of producingtagatose, comprising contacting (a) starch, maltodextrin, sucrose, or acombination thereof; with (b) (i) tagatose-6-phosphate phosphatase, (ii)tagatose-6-phosphate kinase consists of the amino acid sequence of SEQID NO: 3 or 5, (iii) glucose-6-phosphate-isomerase, (iv)phosphoglucomutase or glucokinase, (v) phosphorylase, and (vi) one ormore of α-amylase, pullulanase, isoamylase, glucoamylase, or sucrase;and (c) phosphate.